Niches are not hard to find really, just do some research on certain niches. Niches can come from passions, hobbies, work, school and even home. Try to pick something that you have a "niche" for to make it easier to come up with a way to have unique and up beat submissions. If your forced to do something it gets dull after a while. If you love it in some way you will always have something to say about it.
A niche can make or break a blog or even an entire website. No matter the way its developed. Find out from yourself what would make the best niche for you.